The invention relates to a device for detection of a trapping condition in a power-operated closing element. Devices of this type are used to switch off the drive unit of the closing element and if necessary reverse its movement in the event of a trapping condition arising, e.g. the trapping of a part of the body between two opposite closing edges. These anti-trapping devices are used, for example, on electrically operated window lifters and sliding roofs, automatic vehicle doors, e.g. in buses and trains, as well as in lift doors or the like.
The well-known devices for detection of trapping are based essentially on two different methods of operation.
In a first type of anti-trapping device the information on possible trapping is taken from the power data of the drive unit for the closing element. In the case of electrical drives, for example, this is done by monitoring the motor current or torque output, both of which increase in the event of trapping. If a specific threshold value of the respective parameter is exceeded, the drive motor is switched off and, if necessary, the direction of movement is reversed. Problems are caused in these systems in particular by friction losses of the closing element on guide devices and sealing elements for the closing element. These friction losses are heavily dependent on external factors such as outside temperature or lubrication condition, which leads to wide variation of the monitored drive characteristic values and frequent faulty tripping.
In a second type of anti-trapping device pressure-operated switching elements are used, which are arranged on a closing edge and switch off or reverse the drive unit of the closing element when pressure is applied. LU-A-87 942 describes, for example, an anti-trapping device in which a film pressure sensor is mounted on the closing edge of the closing element. If an obstacle is in the path of movement of the closing element, the film pressure sensor is tripped by direct application of pressure when the obstacle is struck and the drive control of the closing element reverses the direction of movement of the latter. An arrangement of this type is characterised by an extremely high probability of response, but problems are caused in this arrangement by the direct transmission of the trapping force to the active area of the actual switching element. In fact, moving obstacles in particular may exert heavy impacts on the switching element and destroy the latter.
DE-PS-33 47 945 describes a moulding on the closing edge of a moving closing element, in which a closing force is transmitted via several segments, some of which are arranged in a V-shape, to a switching rib. The switching rib is forced in the direction of the closing force on to the switching element and trips the latter by direct application of pressure. Although the closing force is transmitted via segments and a switching rib to the switching element with this moulding, with the result that the actual switching force exerted on the switching element is easily reduced, impacts nevertheless cause significant displacement of the switching rib towards the switching element. However, this in turn produces inadmissibly high direct loading of the active area of the switching element, which leads to its destruction.
Consequently, the task of the present invention is to propose a device for detection of a trapping condition in which direct application of a trapping force to the switching element is prevented.
According to the invention this problem is solved by a device for detection of trapping in a power-operated closing element with a switching element which is arranged along a first closing edge within an elastic hollow section. The hollow section comprises a central area extending longitudinally, in which an active area of the switching element is arranged, and at least one side area extending longitudinally, in which a non-active edge area of the switching element is arranged, the side area on the side of the hollow section facing the first closing edge being more deformable than the central area. The device also has a longitudinally extending force transmitter, which transmits a trapping force essentially at right angles to the side area of the hollow section. It should be noted that the first closing edge may belong to a moving closing element and also to a fixed element which interacts with the closing element when it is closed to close an opening.
Consequently the device according to the invention is characterised by transmission of the trapping force to the side area of the hollow section instead of directly to the active area of the switching element. This ensures that the side area of the hollow section in the area of the point of attachment of the force transmitter is deformed towards the trapping force, the central area largely retaining its shape because of the relatively smaller deformability. The switching element is thus deflected in its edge area towards the trapping force, so that the dimensionally stable central area of the hollow section exerts a switching force on the active area of the switching element, which acts in the opposite direction to the trapping force. If the closing element is withdrawn from the trapping position, which is effected by reversal of the drive device, the trapping force diminishes and the hollow section resumes its original shape because of its elasticity. Consequently the pressure exerted by the central area of the hollow section on the active area of the switching element diminishes, and the switching element opens.
The important advantage of the indirect tripping of the switching element is that the maximum deflection of the edge area of the switching element and thus also the switching force exerted by the central area of the hollow section on the active area of the switching element can easily be limited without impairment of the response of the device. This is done by limiting the maximum deformation of the side area of the hollow section by suitable design of the side area.
The higher deformability of the side area in relation to the central area may be achieved, for example, by making the side area from a softer material than the central area. Suitable material selection and appropriate dimensioning of the thickness of the side area ensure that the side area can initially be deformed very easily, which ensures high response probability but with increasing deformation exerts a greater counter-force and thus limits further deformation.
In an alternative design of the hollow section the central area and side area are made from the same material. In this case the side area has a longitudinal hollow chamber, which absorbs the deformation of the side area, in its wall facing the closing edge. After this hollow chamber has been fully compressed by a trapping force, a side area designed in this way cannot absorb any further deformation.
To allow particularly accurate transmission of the switching force to the active area of the switching element, the central area has a longitudinal elevation, which projects into the hollow space of the hollow section, preferably on the side of the hollow section facing the first closing edge. The switching force exerted by the central area is then transmitted locally by this elevation to the switching element, so that tripping of the switching element already takes place reliably with very small deflection of its edge area. Consequently this measure significantly improves the response of the device.
The hollow space in the central area is preferably curved concavely outwards on its side facing away from the first closing edge. If the side area is deformed by a trapping force, the wall of the hollow space in the side area facing away from the first closing edge may be displaced towards the switching element. Undesirable direct tripping of the switching element can be prevented by the curved design of the hollow space on this wall.
The force transmitter is advantageously connected on the side of the hollow section facing away from the first closing edge in one piece to the side area of the hollow section. Consequently the force transmitter forms with the hollow section a unit which can be easily manufactured and assembled. The connection point of the force transmitter is preferably selected in such a way that lateral deflection of the free end of the force transmitter does not constrict the hollow space of the hollow section.
In a preferred embodiment of the invention the device comprises a spacer, which in an area of the hollow section on the side of the switching element facing away from the first closing edge extends over the latter""s active area. This spacer comprises, for example, an impact buffer made from dimensionally stable material, which extends essentially at right angles to the first closing edge through suitable openings in the hollow section and the switching element, a first end of the impact buffer resting on the first closing edge and a second end of the impact buffer extending beyond the switching element. The second end of the impact buffer may lie within the hollow space of the hollow section or project from the hollow section through a suitable opening in its wall facing away from the first closing edge. This impact buffer prevents a second closing edge, which is opposite the first closing edge when the closing element is closed, from imposing a direct load on the switching element.
In a preferred form of construction the impact buffer comprises a sleeve arranged essentially at right angles to the first closing edge and a rivet, which can be introduced into the sleeve, the inside diameter of the sleeve corresponding essentially to the outside diameter of the rivet shank and the length of the latter being smaller than the depth of the sleeve hole. This two-part design allows the buffer to be assembled particularly easily. In addition an area of the sleeve hole is not filled by the rivet shank after assembly of the impact buffer. If the sleeve is designed with thin walls, this unfilled area of the sleeve imparts a certain flexibility to the impact buffer, so that the closing element is gently braked when the second closing edge strikes the impact buffer. This, of course, has a protective effect on the entire drive mechanism of the closing element on the one hand, and the noise generated when the second closing edge strikes the buffer is clearly reduced on the other.
To prevent direct stressing of the switching element by the second closing edge, the device comprises in an alternative embodiment a spacer in the form of a clamp made from dimensionally stable material, which encloses the hollow section from the side facing away from the closing edge and is supported by the first closing edge. The clamp is preferably designed in such a way that its shape is adapted to the outer shape of the hollow section with a certain clearance, so that the assembled clamp does not exert any pressure on the hollow section wall facing away from the first closing edge. In order to enclose only the hollow section and not the force transmitter, the clamp is guided laterally through suitable openings in the force transmitter, the openings being designed in such a way that transmission of a trapping force is not impaired. The important advantage of the clamp compared to the impact buffer is that the hollow section need not be drilled when fitting the clamp and the hollow space consequently remains tight. This ensures optimum protection of the switching element arranged in the hollow section against dust and other contaminants. With regard to reduction of noise the clamp is preferably made from an elastic material such as metal or plastic.
A particularly advantageous embodiment of the invention is characterised by a second force transmitter extending longitudinally, which is connected on the hollow section side facing away from the first closing edge to a second lateral area and transmits a trapping force essentially at right angles to the second side area of the hollow section, and by a membrane made from flexible material, which extends at a certain distance from the hollow section between the first and second force transmitter. The second closing edge is introduced between the two force transmitters when the closing element is closed and enters the membrane. Firstly, the closing element is braked without imposition of a direct load on the switching element and, secondly, the two force transmitters experience a lateral force in the direction of the second closing edge. This is particularly advantageous if the force transmitters have sealing lips which are simultaneously intended to perform a sealing function against the second closing element. The sealing lip of each force transmitter is pressed firmly against the second closing element by the force acting laterally in the direction of the second closing element, so that the sealing effect is significantly improved.
It should be noted that the use of spacers to avoid direct stressing of the switching element by the closing element is made possible only by the arrangement of the switching element and force transmitter according to the invention. In fact a spacer of this type can be used effectively only if the force transmitter as the tripping element of the device is not arranged directly in the path of the closing element.
The switching element preferably comprises a film pressure sensor known under the name xe2x80x9cforce sensing resistorxe2x80x9d. Sensors of this type consist of two plastics films glued to each other, spacers being affixed between the films. Electrode paths which mesh with each other in the active area of the sensor are mounted on one of the two films. The second film is coated with a semi-conductor polymer, which establishes an electrical contact between the two meshed elect rodes when pressure is applied to the sensor. The higher the pressure applied, the greater the compression of the conductive particles in the polymer and the smaller becomes the resistance of this electrical contact.
A specific embodiment of the invention will now be described below with reference to the enclosed figures. A device for detection of trapping in an electrically operated side window of a motor vehicle is involved.